RT internals documentation?

Does any documentation exist on the internals of RT? What it expects to
find where? There are a number of changes I’m interested in making, and
it would be much easier to do so if I didn’t first have to learn the
entire layout of the system dry from source.

Has anyone here had any experience with having BP do customization
work? Opinions on quality of deliverables, cost, and turn-around time
are appreciated.

Anthony Sorace
Director of Information Technology